What if River is a long time personification of the TARDIS? The 'person whose' identity (soul?) was put into Idris? (Confuses me, Idris is a male name meaning 'impulsive lord', and one for a dragon, at that ) Not sure if it would work, and there are probably a hundred reasons why she can't be, but in terms of meeting the Doctor when she was still 'young', meeting him out of time-sequence, knowing how to pilot the ship better than he does, the deep abiding love she has for him... I could see it. Anyway, I had the thought: discuss!
Interesting thought, but I think it's unlikely. The TARDIS says herself she was a museum piece even when he stole her, so she was hardly young. It would also mean the Doctor was left without a TARDIS at some point in the future but if he were then what were the adventures he and River were having? Unless the TARDIS manages to will a personification in to being. Also, if she's a TARDIS and is now inside the Library computer does that make the Library a TARDIS now?